Which of the following explains why pea plants in high soil nitrogen conditions have so few rhizobial nodules on their roots? When there is already high soil nitrogen there is a very large cost to...

Extracted text: Which of the following explains why pea plants in high soil nitrogen conditions have so few rhizobial nodules on their roots? When there is already high soil nitrogen there is a very large cost to having rhizobial nodules. The rhizobia bacteria in the nodules fix nitrogen when there isn't enough in the soil, so when there is already high soil nitrogen there is no advantage for the pea plant to expend the extra energy housing the rhizobia. The rhizobia bacteria in the nodules use nitrogen when there isn't enough in the soil, so in conditions of high soil nitrogen the plant tries to exclude the rhizobia to keep the nitrogen for itself. When there is already high soil nitrogen there is no benefit to the plant to having rhizobial nodules, which can rob the plant of the high nitrogen supplies so that the rhizobia bacteria do not have to fix the nitrogen themselves.